Dilated Pupils From Drugs: What Causes It and When to Be Concerned

Dilated pupils, medically known as mydriasis, occur when the pupils of the eyes are enlarged beyond their normal size, something that typically occurs under low-light conditions.[1]

But while pupil dilation can be a normal physiological reaction to the environment, it can also be caused by a variety of substances. Being able to recognize when someone’s pupils are enlarged due to drug use is important because it may be one of the first visible signs to others that a person is struggling with substance use. In some cases, it could indicate a medical emergency. Understanding what causes dilated pupils and which drugs produce this reaction may help you get assistance for yourself or someone you care about before the situation gets worse.

What Causes Dilated Pupils From Drug Use?

There are two sets of opposing muscles in each eye that control pupil size, each regulated by the autonomic nervous system, which controls involuntary body functions. The sympathetic nervous system causes pupils to dilate, and the parasympathetic nervous system causes them to constrict.

Drugs that affect neurotransmitters such as dopamine, serotonin, norepinephrine, or acetylcholine can cause pupil dilation by disrupting the balance between the sympathetic and parasympathetic nervous systems.[2] This happens when a drug increases sympathetic activity or blocks parasympathetic activity. How much a person’s pupils dilate will depend on the type of drug, how much is taken, and the person taking it.

Understanding which substances cause pupils to dilate can help someone recognize when a person may be using drugs and needs medical help or intervention.

What Drugs Cause Dilated Pupils?

Stimulants

Stimulants are some of the most common drugs that may cause mydriasis. Cocaine, methamphetamine, and prescription drugs such as Adderall are examples of this drug class. Stimulants work by increasing the availability of neurotransmitters such as dopamine and norepinephrine in the brain, which triggers the sympathetic nervous system and causes significant pupil dilation.[3]

Because methamphetamine is one of the most potent stimulants, its use is particularly linked to mydriasis. People using methamphetamine may have rapid, darting eye movements in addition to significant pupil dilation.

Hallucinogens

Hallucinogens are another major category of drugs strongly associated with mydriasis. Hallucinogens include LSD, psilocybin, and mescaline. They typically affect serotonin receptors (specifically the 5-HT2A receptor in the brain) and can lead to pupil dilation as part of their effects on the central nervous system.[4]

MDMA

MDMA (3,4-methylenedioxymethamphetamine), commonly known as ecstasy or molly, is a drug that causes a significant release of serotonin, dopamine, and norepinephrine, all of which contribute to mydriasis.[5] Mydriasis is one of the most obvious physical effects of MDMA use and can persist for hours following use.
The effect of MDMA on the serotonin system increases the risk of developing serotonin syndrome, a severe complication resulting from excessive serotonin stimulation, when used in conjunction with other serotonergic medications such as selective serotonin reuptake inhibitors (SSRIs) or other antidepressants.

 

Anticholinergic Drugs

Anticholinergic substances block the neurotransmitter acetylcholine, which is responsible for activating the parasympathetic nervous system. When parasympathetic signals are blocked, the sympathetic nervous system will take over, causing pupil dilation and other effects.

There are a number of different types of drugs that have anticholinergic effects, including many prescription medications. Some antihistamines, such as diphenhydramine (the active ingredient in Benadryl), and some decongestants may produce anticholinergic effects. Signs and symptoms of anticholinergic toxicity include dilated pupils, dry mouth, flushing, rapid heart rate, confusion, and urinary retention.[6]

Inhalants

Illicitly used inhalants cause mydriasis via toxicity to the central nervous system, activation of the sympathetic nervous system, or by causing hypoxia (lack of oxygen).[7] These include xylene- and toluene-containing solvents, found in spray paint, glue, gasoline, paint thinner, and paint stripper. They are also found in industrial cleaners, degreasers, and automotive solvents. Nitrous oxide is another inhalant associated with mydriasis by causing hypoxia.

Prescription Medications

There are some prescription medications that can cause dilated pupils as a side effect, even when taken as directed. These include some classes of antidepressants, decongestants (like Sudafed), and medications used in ophthalmology for eye exams. The effects on pupils would be more pronounced if these medications were misused or taken at dosages greater than directed.[8]

SSRIs and serotonin-norepinephrine reuptake inhibitors (SNRIs) can produce mild mydriasis as a result of their effect on serotonin levels. This is important to consider when combining SSRIs or SNRIs with other serotonergic agents, as the risk for serotonin syndrome and more severe mydriasis greatly increases.

Dilated Pupils vs. Pinpoint Pupils

Not all drugs will produce dilated pupils. Opioids such as heroin, fentanyl, oxycodone, and hydrocodone produce the opposite effect. These drugs cause miosis, which is pinpoint pupils that are extremely constricted, typically measuring less than two millimeters in diameter, and which do not respond normally to light.[9] Opioids produce miosis because they activate the parasympathetic nervous system by interacting with opioid receptors.

Miosis is a classic sign of opioid intoxication and overdose. When you see an individual with pinpoint pupils, coupled with respiratory depression, unresponsiveness to stimuli, and cyanosis (blue-tinged lips or fingers due to lack of oxygen), this is a medical emergency, and medical assistance must be sought immediately. If naloxone is available, it should also be administered.

Understanding the difference between dilated and pinpoint pupils and the substances that cause each is critical in an overdose situation.

When Are Dilated Pupils a Sign of Danger?

Dilated pupils by themselves will not always be a sign of a medical emergency. However, if someone has dilated pupils with one or more of the following conditions, seek emergency care:

• Extremely rapid or irregular heart rate
• Severely elevated blood pressure
• High body temperature with profuse sweating
• Muscle rigidity or twitching
• Seizures
• Severe confusion, agitation, or loss of consciousness
• Difficulty breathing

These symptoms, when present together, can indicate serotonin syndrome, stimulant overdose, anticholinergic toxicity, or another medical emergency related to drug use. The classic signs of serotonin syndrome specifically include agitation, tachycardia, elevated blood pressure, mydriasis, muscle twitching or rigidity, and, in severe cases, seizures or loss of consciousness.

It is also important to note that mydriasis can occur as a result of non-drug-related events. Brain injuries and conditions affecting the central nervous system may also produce mydriasis and require a medical evaluation if it occurs abruptly or the cause of the mydriasis is unknown.

Recognizing Drug Use in Someone You Care About

Changes in pupil size are just one of several physical signs of drug use. If you are close to someone with a substance use problem, you may notice several other physical signs as well, including:

• Changes in sleep patterns
• Sudden weight gain or loss
• Mood or behavior changes
• Withdrawal from previous relationships and responsibilities
• Declining performance at work or school
• Isolation
• Secretiveness
• Becoming careless with physical appearance

If you are concerned about someone you care about, it is important that you have a compassionate and non-judgmental conversation with them. Substance use disorder is a multi-faceted condition, not a moral failure. Encouraging your loved one to seek out a health professional or a treatment program is the most supportive action you can take.

Getting Help for Substance Use Disorder in Fort Lauderdale

Whether you are concerned about your own substance use or that of someone you care about, Agape Treatment Center is here to help. Our outpatient treatment programs offer evidence-based (practical application of the findings of the best available current research) care for substance use disorder and co-occurring mental health conditions, tailored to each person’s needs. Get started today to take the first step toward lasting recovery.

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